1. Field of the Invention
The present invention relates to a form measuring instrument such as a roundness measuring machine which measures a displacement in synchronization with an angular position of rotation of a workpiece that is rotating about a specified rotation axis, a form measuring method, and a program.
2. Description of the Related Art
Conventionally, there has been known a roundness measuring machine which receives a workpiece on its table, rotates the table, and makes a measuring probe (a contact piece) scan the surface of the workpiece (see JPH5-231864A, JP2551698B). Such a roundness measuring machine has to have the contact piece calibrated in an X-axis direction and a Y-axis direction, so that the center of the workpiece may be aligned (centered) with the rotation axis of the table.
Currently, centering is performed by best-fitting data obtained by concentrically measuring an aspheric workpiece to aspheric surface design values. At this time, if the off-centering value of the workpiece is large, a radial position that is outside the range of a design value might be measured or an error contained in a detected value might become large. Therefore, the workpiece might stick out from the measuring region which the machine is guaranteed. In this case, the workpiece and the measuring machine might be damaged.